The liver is a huge and metabolically active organ, enriched with substantial numbers of non-conventional immune cells that help to protect it from pathogens and potentially harmful immune responses to benign foreign material (such as antigens in food). Particularly striking are the many natural killer T (NKT) cells, which likely serve to regulate hepatic immunity.

To examine the behavior of hepatic NKT cells in situ, Geissmann et al. used mice in which one of the alleles coding for the NKT chemokine receptor CXCR6 had been replaced with green fluorescent protein. Intravital confocal microscopy revealed that NKT cells remained confined to the blood vessels within the liver, moving randomly and visiting each hepatocyte every quarter of an hour. This behavior differs from that of conventional activated T cells, which generally pass across the vessel endothelium into the surrounding tissue. Nevertheless, as do T cells on patrol in lymph nodes, hepatic NKT cells stop moving upon encountering antigen, consistent with their surveillance duties. In the absence of CXCR6, the number of hepatic NKT cells was significantly reduced, suggesting that this chemokine receptor mediates a survival signal. — SJS